Cerebral autoregulation (CA) is a critical process for the maintenance of cerebral blood flow and oxygenation. Assessment of CA is frequently used for experimental research and in the diagnosis, monitoring, or prognosis of cerebrovascular disease; however, despite the extensive use and reference to static CA, a valid quantification of "normal" CA has not been clearly identified. While controlling for the influence of arterial PCO 2 , we provide the first clear examination of static CA in

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... humans over a wide range of blood pressure. In 11 healthy humans, beat-to-beat blood pressure (radial arterial), middle cerebral artery blood velocity (MCAv; transcranial Doppler ultrasound), end-tidal PCO 2 , and cerebral oxygenation (near infrared spectroscopy) were recorded continuously during pharmacological-induced changes in mean blood pressure. In a randomized order, steady-state decreases and increases in mean blood pressure (8 to 14 levels; range: Ϸ40 to Ϸ125 mm Hg) were achieved using intravenous infusions of sodium nitroprusside or phenylephrine, respectively. MCAv mean was altered by 0.82Ϯ0.35% per millimeter of mercury change in mean blood pressure (R 2 ϭ0.82). Changes in cortical oxygenation index were inversely related to changes in mean blood pressure (slopeϭϪ0.18%/mm Hg; R 2 ϭ0.60) and MCAv mean (slopeϭϪ0.26%/cm ⅐ s Ϫ1 ; R 2 ϭ0.54). There was a progressive increase in MCAv pulsatility with hypotension. These findings indicate that cerebral blood flow closely follows pharmacological-induced changes in blood pressure in otherwise healthy humans. Thus, a finite slope of the plateau region does not necessarily imply a defective CA. Moreover, with progressive hypotension and hypertension there are differential changes in cerebral oxygenation and MCAv mean . (Hypertension. 2010;55:698-705.)